1. Field of the Invention
This invention relates to a projection type image display apparatus for enlarging and projecting an image onto, for example, a screen.
2. Description of the Related Art
A three-panel type liquid crystal projector is known as a liquid crystal projector in which white light emitted from a light source is separated into three colors (red, green, and blue) by a wavelength-selectable dielectric memberane, rays of light that have passed through their respective liquid crystal panels (image forming panels) are thereafter synthesized by a dielectric memberane so as to produce a color image by use of three monochromatic-liquid crystal panels, and the color image is enlarged and projected onto, for example, a screen through a projection lens.
A high intensity lamp, such as an extra-high pressure mercury lamp, is used as the light source of a liquid crystal projector, and the reflector surface of the lamp reaches a high temperature.
The liquid crystal panel also undergoes a rise in temperature by being illuminated with light from the light source. The liquid crystal panel is illuminated by polarized light, and polarizing plates are used on the incident and outgoing sides of the liquid crystal panel as a pair.
In most cases, the polarizing plate to be used is a film type due to cost, but this is inferior to crystal in transmittance, and easily absorbs light in the form of heat. Additionally, polarized light is absorbed by the polarizing plate and is changed into heat when light in which a polarization plane rotates with respect to the transmitted-light axis of a polarizing plate by driving the liquid crystal passing through the polarizing plate.
Accordingly, there is a fear that display contrast will be lowered by heat if the heat absorbed by the liquid crystal panel and the polarizing plate as described above is not lowered by cooling from the outside in order to use them below a temperature at which reliability can be kept.
Therefore, there exist a method for, as disclosed in Japanese Patent No. 2860989 shown in FIG. 7, disposing an axial fan 102 under a dichroic prism 101 used for color synthesis and cooling three color liquid crystal panels 103 simultaneously, and a method for, as proposed in Japanese Laid-open Patent No. H05-53200 shown in FIG. 8, providing a sirocco fan 104 and an air chamber 106 used to supply air drawn by the fan to the three color panels 103.
In general, the respective rays of light separated into red, green, and blue are different from each other in quantity, and are different therefrom in heat distribution in the image forming panel. In the method disclosed in Japanese Patent No. 2860989 mentioned above, the three panels 103 are cooled by the single axial fan 102, and therefore, if the rotational speed of the fan is set according to an optical path that has a high exothermic energy in a case where the exothermic energy of the optical path is much higher than those of other optical paths, then the other optical paths will be excessively cooled. This is disadvantageous from the viewpoint of cooling efficiency.
In the method proposed in Japanese Laid-open Patent No. H05-53200 mentioned above, three optical paths share the fan with each other, and therefore it is extremely difficult to prepare a flow path design that considers the balance of a cooling capacity in the three color optical paths.
Additionally, in both of the methods, as shown in FIG. 9, openings 108 or shape of nozzles from which an air current is expelled are disposed in the vicinity of the liquid crystal panels 103 and the polarizing plates 107 attached to the prism 101, which are to be cooled. However, since cooling conditions and cooling balance in each optical path depend greatly on the size of the openings 108 or on the shape of the nozzle, trial and error through experimentation must be carried out to determine the size or shape of the openings 108 and nozzles.
In other words, a problem resides in the fact that air capacity can be enlarged by widening the openings 108, but on the contrary, if the openings 108 are narrowed, not only will air capacity decrease but also an area to which the cooling air is supplied will decrease.
Another problem resides in the fact that a higher cooling capacity is needed proportionately with a rise in brightness of the liquid crystal projector, and, as a result, the cooling fan and the air chamber become larger in size.
Therefore, in order to realize a size reduction and a noise reduction of the apparatus, there is a need to cool the apparatus more efficiently, and it has become extremely important to determine the cooling conditions and the cooling balance in each color optical path.
It is, therefore, an object of the present invention to provide a projection type image display apparatus whose optical elements, such as an image forming panel, a polarizing plate, and a prism disposed in each color optical path, are designed to be cooled efficiently.
In order to achieve the object, a projection type image display apparatus by which a color image is projected and displayed according to the present invention includes a color separation optical system which separates illumination light into a plurality of chromatic rays of light, a plurality of image forming panels illuminated with the plurality of chromatic rays of light, respectively, a color synthesizing optical system which synthesizes rays of light emitted from the plurality of image forming panels illuminated therewith, and a plurality of cooling units which cool areas around the plurality of image forming panels, respectively, in which a cooling capacity of at least one of the plurality of cooling units is different from those of the other cooling units.
For example, the plurality of cooling units are the same in kind, and the specifications of at least one of the cooling units differ from those of the other cooling units. In greater detail, the air capacity of an air-blowing fan is made different, or the shape of a duct by which the air current from the air-blowing fan is guided to areas around the image forming panels is made different from the other ones.
Alternatively, the kind of at least one of the cooling units can be made different from those of the other cooling units. In greater detail, an axial fan and a sirocco fan are used. Alternatively, a fan and a thermoelectric exchange element, such as a Peltier element, can be used.
If a polarizing element is disposed in the vicinity of each image forming panel (e.g., LCD panel), the polarizing element can also be cooled by each cooling unit.
In order to achieve the object, a projection type image display apparatus by which a color image is projected and displayed according to the present invention includes a color separation optical system which separates illumination light into a plurality of chromatic rays of light, a plurality of image forming panels to be illuminated with the plurality of chromatic rays of light, respectively, a color synthesizing optical system which synthesizes rays of light emitted from the plurality of image forming panels illuminated therewith, a plurality of cooling units which cool areas around the plurality of image forming panels, respectively, and a control circuit which controls the plurality of cooling units, in which the control circuit controls at least one of the plurality of cooling units independently of the other cooling units.
For example, if the plurality of cooling units each have an air-blowing fan, at least one of the air-blowing fans can be controlled so that the revolving speed of at least one differs from those of the other air-blowing fans.
Further, if there is provided a light-quantity changing member which changes the quantity of chromatic light that strikes at least one of the image forming panels, one of the cooling units that cools the image forming panel can be controlled in a different manner from a manner in which the other cooling units are controlled in accordance with a change in the quantity of incident light upon the image forming panel caused by the light-quantity changing member.
In this case, if a polarizing element is disposed in the vicinity of each image forming panel, the polarizing element can be cooled by each cooling unit in the same manner as above.
A detailed configuration of the projection type image display apparatus of the invention, the above and other objects and features of the invention will be apparent from the embodiments, described below.